Peptides having alkyl- and dialkylguanidinyl-containing side chains or imidazolinylamino- or tetrahydropyrimidinylamino-containing side chains are frequently useful as pharmaceutical agents. Typically these peptides have been produced by first synthesizing the individual amino acids containing the desired side-chain modification, protecting the reactive side-chain groups in the various amino acids, and subsequently linking the individual modified amino acids to a resin form a peptide using conventional methods. This conventional method is the solid phase method set forth in Merrifield, R. B. J. Am Chem. Soc. 1963, 85, 2149. This process of first synthesizing the protected amino acids containing the desired side chain modification and then synthesizing the peptide is typically a difficult and expensive one, often yielding relatively small amounts of the desired peptide. There is thus a need in the an for a process whereby peptides containing imidazolinylamino- or tetrahydropyrimidinylamino-containing side chains or alkylguanidinyl or dialkylguanidinyl-containing side chains can be more readily introduced into peptides using solid phase peptide synthesis techniques.